1. Field of the Invention
This invention relates to a seat slide mechanism for vehicles, particularly to a seat slide mechanism having an upper rail slidable with respect to a lower rail fixed to a vehicle floor and being provided for the fore-and-aft adjustment of the seat of the vehicle.
2. Description of the Prior Art
Japanese Laid Open (KOKAI) Publication No. 112729/1991 describes a seat slide mechanism having an upper rail for attachment to a seat cushion frame, a lower rail secured to the vehicle floor, a screw nut assembly for sliding the upper rail in the fore-and-aft direction along the lower rail by actuating an electric motor so as to ensure a desired attitude of the seated individual, and rollers or balls disposed in a space formed by both the rails to contact the surfaces thereof and decrease the sliding friction between both the rails.
The upper rail is of a generally inverted U-shaped cross section and the lower rail is of a generally U-shaped cross section. The rollers are arranged in spaces formed at front and rear portions of the inverted U-shaped body in section and the U-shaped body in section of both the opposed rails. The balls are disposed in a space between opposed lateral elongations of the upper rail and the lower rail to slidably contact these elongations through the balls.
The front rollers are laterally spaced and positioned at a portion in advance of the nut member of the screw nut assembly so that the screw member of the screw nut assembly is free from the front rollers. Therefore, for the purpose of arranging the space for the front rollers, the front portion of the lower rail must be extended in a forward direction as long as possible.
The movement of the front rollers is independent of the movement of the rear rollers and these movements of the rollers are free from the roll of the balls, so that the dimensions between the rollers or relative positions of the rollers and the balls are not kept constant and the upper rail will not slide smoothly with respect to the lower rail.